Apparatus for producing high frequency vibrations of a sieve screen

ABSTRACT

In apparatus for producing high frequency vibrations of a seive screen and composed of a vibratory system including a rod which extends transverse to the screen surface and is attached to the screen at a point, and an electromagnetic vibration generator which acts on the rod and applies thereto vibrations which in turn are transferred to the screen, the rod is connected to a rubber return spring which is tuned to the vibratory system.

United States Patent 1191 1111 3,751,694 Erlenstaedt 1 Aug. 7, 1973 APPARATUS FOR PRODUCING HIGH 2,880,871 4/1959 Bruninghaus 310 29 ux FREQUENCY VIBRATIONS OF A SKEVE 3,333,219 7/1967 Maklno 310/29 SCREEN 3,522,460 8/1970 Spurlm 310/29 H I 7 2,814,429 11/1957 Buchanan 310/29 [75] Inventor: Giinter Erlenstaedt, Remscheid, 3,330,411 7/1967 Erlehstadt 209/368 Germany 2,865,505 12/1958 Bruninghaus 209/310 u ,9 [73] Assignee. Rhewum Rhenmsche Wer'zeug Primary Examiner R Skudy Machmenfabnk GmbH, Remscheid- Attorney-George H. Spencer et a1. Luttrmghausen, Germany [22] Filed: Aug. 26, 1971 [211 App]. 175,204 in appaiatus for producing high frequency vibrations of a seive screen and composed of a vibratory system in- [30] Foreign Application Priority Data eluding a rod which extends transverse to the screen Apr. 26, 1971 Germany P 21 20 244,3 surface and is attached to the screen at a point, and an electromagnetic vibration generator which acts on the [52] US. Cl 310/29, 209/310, 209/368 r d and applies thereto vibrations which in turn are [51] Int. Cl. H02k 35/00 tran f rred to the screen, the rod is connected to a rub- [58] Field of Search 310/29, 81, 30, 34; ber return spring which is tuned to the vibratory sys- 209/310, 368 tem.

[56] References Cited 9 Claims, 3 Drawing Figures UNITED STATES PATENTS 3,121,679 2/1964 Newberg 209/310 a; 1 re-V APPARATUS FOR PRODUCING HIGH FREQUENCY VIBRATIONS OF A SIEVE SCREEN BACKGROUND OF THE INVENTION The present invention relates to apparatus for producing high frequency vibrations of a sieve screen.

In known types of sieve screen vibration devices which include a return spring and a rod engaging the sieve, the return spring is made of steel. The steel spring is tuned to a natural frequency which lies outside of the critical frequency of the sieve screen in order to keep damage to the sieve screen'due to resonance as low as possible.

These devices, however, have the drawback that a change in the excitation frequency and/or a change in the mass of the material which is placed onto the screen by the addition or subtraction of amounts of material therefrom destroys the preselected tuning of the steel spring. As a result, it is necessary in sieve devices provided with the known apparatus, to replace the return spring whenever the excitation frequency and/or the material mass is changed in order to produce a sifting effect which is optimized for the particular material to be sifted.

It has further been found that harmonic vibrations are produced at the sieve screen when the rod is limited in its striking amplitude. The frequencies of these harmonies in known devices are approximately twelve times as high as the fundamental frequencies.

Also with known devices, increase in the voltage applied to the electromagnetic vibration, generator will increase the amplitude of the vibration when necessary in response to, for example, changes in the material to be sifted. However, these known devices can only increase vibration amplitudes up to approximately twothirds of the rated generator voltage.

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a device for producing high frequency vibrations on a sieve screen of the above-identified type in which variations in the excitation frequencies and/or changes in material mass over a wide range can be achieved without danger to the sieve screen and without requiring replacement of the return spring.

It is another object of the present invention to provide a device for producing high frequency vibrations on a sieve screen of the above-identified type in which vairations in the excitation frequencies and/or changes in material mass over a wide range can be achieved with a single return spring.

These and other objects are achieved according to the present invention by the provision of a rubber spring as the rod return spring which is preferably designed as a bending spring:

The rubber spring is in the form of a block-shaped rubber bending spring in which the ratio of length to width to thickness is approximately 3:4:] and wherein preferably the rubber bending spring has a Shore hardness in the range of 50 to 55. The generator armature is adhered to the rubber spring during the vulcanization thereof. The armature is characterized in that it is provided along its longitudinal axis with a threaded bore. The threaded bore receives therein an end portion of the rod, which has a shape corresponding with the threaded bore. The rubber spring is provided with a passage for the rod on the side facing away from the electromagnetic vibration generator, the passage being disposed coaxially with the threaded bore.

The present invention has the advantage that the preselected excitation fundamental frequency of, e.g. Hz, can be lowered to about 50 Hz or raised to about Hz without requiring retuning of the spring, while in the known devices which are tuned for example to 100 Hz, deviations of: 10 Hz require returning of the spring.

Another advantage of the present invention is that harmonic frequencies as high as eighteen times the fundamental frequency can be imparted to the sieve screen. This represents a significant increase over that permitted in prior known devices.

A further advantage is that with an increase of the voltage applied to the electromagnetic vibration generator to adapt the amplitude of the vibrations to the material to be sifted, in the apparatus according to the present invention the vibration amplitude increases linearly with the increase in voltage until the rated voltage is reached and not just a fraction of the rated voltage as in the prior art devices.

Still another advantage of the present invention resides in the fact that the generator armature is disposed along the longitudinal axis of the rubber bending spring and over the entire width of the rubber bending spring. The armature has a rectangular cross section. The ratio of the cross-sectional width to the cross-section height of the armature is about 2tl, with the surface of the armature facing the electromagnetic vibration generator being disposed flush with the rubber spring surface fac ing in the same direction.

Yet another advantage results due to the fact that inherently stable strips are adhered to the two longitudinal end portions of the rubber bending spring during the vulcanization thereof.

The strips are made of steel, but any other material may be used as long as it presents almost the same structural stability as steel.

These strips extend over the entire length of the spring and are preferably releasably fastened to an opening in the generator housing. The generator housing is designed in a known cup shape. Thus, the previously required housing cover in the form of a fastening flange can be eliminated.

It is particularly advantageous for the rubber spring to be provided, at least along the surface facing the sieve screen and the sides thereof, with a preferably one-piece cover of elastic material which has an opening therein for the passage therethrough of the rod. The edge portion of the passage is adapted to be in close contact with the rod. In this way, the entire device is tightly sealed against the entry of dust and other foreign particles.

A variation which might be preferred, under certain circumstances, is characterized in that the strips which are adhered to the vulcanized rubber bending spring are clamped between the edge portions of the generator housing opening and a housing cover therefor. The rod in this case passes through the cover and is sealed against the cover opening in a known manner.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation view partly in cross-section of a device according to the present invention for producing high frequency vibrations on a sieve screen.

FIG. 2 is a plan view of another embodiment according to the present invention.

FIG. 3 is a partial view in cross-section taken along line 3-3 of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a carrier 1 is mounted to a stand 1' and an electromagnetic vibration generator 2 is supported by the stand 1 and causes a sieve screen 4 fastened to the stand 1' to vibrate. The vibrations set up by the generator 2 are transferred to the sieve screen 4 by a rectangular rod 3 which is fastened at one end 3' t the screen 4 and at the other end 3" to the armature 8 of the generator 2.

The electromagnetic vibration generator 2 consists essentially of a cup-shaped housing 5, a housing cover 6, an electromagnet 7, an armature 8 which coacts with the electromagnet 7 and a rubber bending spring 9. The rubber bending spring 9 serves as a return spring for the armature 8.

The rubber bending spring 9 has preferably a rectangular block shape. In order to obtain the desired flexural characteristics of the spring 9, it has been found that a length to width to thickness ratio of 3:411 and a Shore hardness between 50 and 55 is desirable. That is, with these parameters a preselected generator excitation frequency of, for example, 100 Hz can be lowered to about 50 Hz or raised to about 150 Hz without requiring retuning or replacement of the spring 9. The spring 9 has been found to satisfactorily return the rod 3 to its null position established prior to excitation for frequency values throughout the stated range.

The armature 8 is mounted within and adhered to the rubber spring 9 during the vulcanization thereof such that its surface 8 facing the electromagnet 7 is at least approximately flush with the surface 9' of the rubber spring 9 facing in the same direction. These surfaces, or at least the surface 8', are recessed with respect to the plane A-A to define thereby a gap 20. The gap 20 is of a sufficient depth to allow the armature 8 to vibrate. The armature 8 has a rectangular cross section and in the direction normal to the plane of FIG. 1 is coextensive with the rubber spring 9.

In the center of the armature 8 a threaded bore 10 is disposed into which a threaded pin 11 at the other end 3" of the rod 3 is thereby engaged.

Coaxially disposed with the threaded bore 10 is an opening 12 in the spring 9. The opening 12 is provided for the rod 3. An elastic annular seal 13 having a hub portion 13' enclosing the rod 3 is disposed within an aligned opening of the housing cover 6. The seal 13 is clamped at its edge portions between the housing cover 6 and the carrier 1, as is an elastic layer 19 having an opening 18 in which seal 13 is disposed.

Steel strips 14 having a rectangular cross section are adhered to the longitudinal edge portions of the rubber spring 9 during the vulcanization thereof. These strips extend over the entire width of the rubber bending spring 9 and are clamped against the shoulders 6' by the inside edge of the flange 5.

The lower end portion 3 of rod 3 is detachably fastened in a known manner to the sieve screen 4. Also, a connecting box 15 for the electrical line (not shown) is provided at the housing 5. In addition, devices (not shown) for varying the voltage supply and its frequency are connected in a known manner to the electromagnet 7.

The electromagnet 7 is fed with a single-phase alternating current having a frequency of about 50 Hz and is designed for a maximum voltage of 220 V. For a force of about 25 kiloponds exerted by the electromagnet 7 on the rubber spring 9, the spring has a length between strips 14 of approximately mm, a width normal to the plane of FIG. 1 of approximately mm and a thickness of approximately 22 mm. The Shore hardness is within the range of 50-55. The armature, however, is about 90 mm wide, about 32 mm long and about 18 mm thick.

FIGS. 2 and 3 show a rubber spring 9 according to the present invention with strips 14 provided with screw holes 16 (shown schematically by center-lines in FIG. 3) for connecting the rubber spring 9 and strips 14 to the housing element 5 and 6 as well as to the frame 1.

So that no dust and/or humidity can enter into the interior of the electromagnet housing, a cap-type cover 17 of an elastic material such as rubber is provided which extends over the entire frontal face of the rubber spring 9 and strips 14 facing the sieve screen 4 and which is provided with frame-type edge portions 17 which are in close contact with the outer sides of strips 14.

Although rubber springs per se are known, the art has thus far considered the use of rubber springs for the above-described type of apparatus as practically impossible because of the relatively high inherent damping of rubber springs.

As a result of the present invention, however, the opposite has been found to be true. The rubber spring according to the present invention has proven highly successful to achieve the desired range of application without requiring frequent changes for returning.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

I claim:

1. In apparatus for producing high frequency vibrations on a sieve screen and comprising a vibratory system including a rod contacting with one end thereof the sieve screen at a point, a vibration generator having an armature which engages the rod for transferring vibrations thereto, and a return spring connected for returning the rod to a null position and tuned to the vibratory system, the improvement wherein said return spring is of vulcanized rubber, said generator is electromagnetic, said armature is disposed in the center of the longitudinal extent of said rubber spring, and is mounted within said spring and adhered thereto, said armature is provided with a threaded bore in the center of its longitudinal extent, said rubber spring is provided, on the side facing away from the generator, with a passage which is disposed coaxially with the threaded bore of said armature, said rod is threaded at its other end, and said other end of said rod is received through said passage and into threaded engagement with said bore.

2. Apparatus as defined in claim 1 wherein said rubber return spring is a bending spring.

3. Apparatus as defined in claim 2, wherein said rubber bearing spring is in the form of a rectangular parallelepiped and the ratio of length to width to thickness thereof is approximately 3:4:1, and wherein said rubber spring preferably has a Shore hardness in the range of 50 to 55.

4. Apparatus as defined in claim 1, wherein said generator has a cup-shaped housing portion, and further comprising stabilizing strips adhered to both longitudinal end portions of said rubber spring said strips extending over the entire length of said spring and being releasably fastened to said housing.

5. Apparatus as defined in claim 4, wherein said rubber spring and said stabilizing strips are provided, at least on their surfaces facing the sieve screen and along the sides'thereof with a cover of an elastic material with a passage therein for said rod, the edge portions of said passage being in contact with said rod.

6. Apparatus as defined in claim 5, wherein said stabilizing strips and said rubber spring are clamped between the housing and a housing cover of said generator, and wherein said rod passes through said housing cover and is sealed with respect thereto.

7. Apparatus as defined in claim 1 wherein said armature extends over the entire width of said rubber spring.

8. Apparatus as defined in claim 1, wherein the armature has a rectangular cross section, said ratio of the 

1. In apparatus for producing high frequency vibrations on a sieve screen and comprising a vibratory system including a rod contacting with one end thereof the sieve screen at a point, a vibration generator having an armature which engages the rod for transferring vibrations thereto, and a return spring connected for returning the rod to a null position and tuned to the vibratory system, the improvement wherein said return spring is of vulcanized rubber, said generator is electromagnetic, said armature is disposed in the center of the longitudinal extent of said rubber spring, and is mounted within said spring and adhered thereto, said armature is provided with a threaded bore in the center of its longitudinal extent, said rubber spring is provided, on the side facing away from the generator, with a passage which is disposed coaxially with the threaded bore of said armature, said rod is threaded at its other end, and said other end of said rod is received through said passage and into threaded engagement with said bore.
 2. Apparatus as defined in claim 1 wherein said rubber return spring is a bending spring.
 3. Apparatus as defined in claim 2, wherein said rubber bearing spring is in the form of a rectangular parallelepiped and the ratio of length to width to thickness thereof is approximately 3: 4:1, and wherein said rubber spring preferably has a Shore hardness in the range of 50 to
 55. 4. Apparatus as defined in claim 1, wherein said generator has a cup-shaped housing portion, and further comprising stabilizing strips adhered to both longitudinal end portions of said rubber spring said strips extending over the entire length of said spring and being releasably fastened to said housing.
 5. Apparatus as defined in claim 4, wherein said rubber spring and said stabilizing strips are provided, at least on their surfaces facing the sieve screen and along the sides thereof with a cover of an elastic material with a passage therein for said rod, the edge portions of said passage being in contact with said rod.
 6. Apparatus as defined in claim 5, wherein said stabilizing strips and said rubber spring are clamped between the housing and a housing cover of said generator, and wherein said rod passes through said housing cover and is sealed with respect thereto.
 7. Apparatus as defined in claim 1 wherein said armature extends over the entire width of said rubber spring.
 8. Apparatus as defined in claim 1, wherein the armature has a rectangular cross section, said ratio of the cross-sectional length to the cross-sectional thickness is approximately 2:1 and the surface of said armature facing said generator is arranged to be flush with the surface of said rubber spring facing in the same direction.
 9. Apparatus as defined in claim 1, wherein said rubber return spring constitutes means for returning said rod to said null position for a range of excitation frequencies of said generator extending from 50 to 150 Hz. 